This page contains a few rules on the TIGGE parameters. A complete list of all the parameters and sample GRIB2 encoding is given here.
Units
- All fields should use units as defined in GRIB Edition 2
Accumulations
- All accumulations should start from the beginning of the forecast
- The initial state (forecast step zero) must be a part of all forecasts, all members, etc ... .
- The values of accumulated fields must be set to zero for t=0
Fluxes
- The flux sign convention will be positive downwards.
Missing values
Bitmaps should be used to indicate missing values (i.e. Soil moisture (sm) must be coded using a bitmap, because there is no model output over the sea)
Grid and resolution
Each partner will provide their eps data on the grid of their choice, although regular grids are favoured. Partners are encouraged to provide also their deterministic forecast (as additional control) projected on the same horizontal grid and resolution as the ensemble members.
Grids are defined in GRIB2 using an accuracy of 1/1000000 (one millionth) of a degree. If this accuracy is not sufficient to describe your grid (latitude/longitude of first and last points, as well as grid increments) without loss of information, you can use a GRIB2 feature that provides a way to describe any regular grid. See the page on encoding global latitude/longitude grid for more details.
Number of forecasts
- The Control Forecast must be number 0,
- The number of members is identical to the number of all EPS members plus the Control Forecast.
GRIB issues
TIGGE Production status of processed data
Octect 36 of section 1 of a GRIB2 message contains the Production status of processed data. The WMO has added two values to table 1.3 Production status of data:
- 4: TIGGE operational products
- 5: TIGGE test products
You should use value 5 when testing (and set the vvvv part of the file naming convention to test), and 4 for operational data (in this case vvvvshould be set to prod).
TIGGE extension (Section 2)
It is proposed that the section 2 for TIGGE fields be the same for all partners. A GRIB2 decoder must decode the section 2 as a TIGGE extension based on the octect 36 of section 1 (Production status of processed data) being 4 or 5.
The format of the TIGGE extension is not yet defined. The section 2 should either be missing or empty.